That's almost certainly the source of the problem. Age can be another factor. Shorts don't last forever. I have had several pairs of PI bibs that have, over time, lost their elasticity in the croch, allowing for uncomfortable junk shifting.

They wear out other places, too. I will never forget the first day of my first Cycle Oregon. A woman rode past me and politely said something like "Your shorts must be really old." They were very old, but I couldn't figure out how she knew that. Then it hit me after about 30 seconds. At the end of the day's ride I inspected them and tossed them in the trash. I have a friend who I sometimes ride with. Despite being well off, he's cheap. He has at least one pair of shorts that provide a nice view of his crack. He needs to be told.